This excellent poem by William Blake concerns anger that is allowed to grow and fester and also the way that we often nurture and hold such anger close to our hearts, refusing to resolve or express it. The poem therefore describes what happens when such anger is left unresolved, symbolically turning that anger into a tree:

And I watered it in fears,

Night and morning with my tears;

And I sunned it with smiles,

And with soft deceitful wiles.

Anger is thus transformed into a tree that is cared for, watered, and nurtured by the speaker, until it bears an "apple bright" which the speaker's foe steals and eats, killing him. It is important to see how this apple and the tree function symbolically. The apple seems to symbolise a harmful or evil action taken by the speaker. The tree itself symbolises the anger and malice that motivated the action, resulting in the death of the enemy. Of course, the tragic truth of this poem is that both the enemy and the speaker have been "poisoned" by the anger, as the speaker is consumed and harmed by his anger.